This thesis addresses real-time rendering techniques for 3D Information-Lenses, which are based on the focus & context metaphor. It analyzes, conceives, implements and reviews its applicability to objects and structures of virtual 3D city models. In contradiction to digital terrain models, the application of focus & context visualization to virtual 3D city models is barely researched. However, the purposeful visualization of contextual data of is extreme importance for the interactive exploration and analysis of this field. Programmable hardware enables the implementation of new lens-techniques, which allows the augmentation of the perceptive and cognitive quality of the visualization, compared to classical perspective projections. A set of 3D information-lenses is integrated into a 3D scene graph system: 1.) Occlusion Lenses modify the appearance of virtual 3D city-model objects in order to resolve their occlusion and consequently facilitate the navigation. 2.) Best-View Lenses display city-model objects in a priority-based manner and mediate their meta-information. Thus, they support exploration and navigation of virtual 3D-city-models. 3.) Color and deformation lenses modify the appearance and geometry of 3D city-models to facilitate their perception. The present techniques for 3D information lenses and the application to virtual 3D city models clarify their potential for interactive visualization and form a base for further development.